Vaccines Rarely Cause Life-Threatening Allergic Reactions: CDC

Just 33 people from 25 million immunized were affected, researchers report

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Just 33 people had a serious, potentially life-threatening allergic reaction -- also known as anaphylaxis -- out of 25 million vaccines given, according to research from the U.S. Centers for Disease Control and Prevention. That's 1.3 people in every million who gets a vaccine.

"Vaccination is one of the best ways parents can protect infants, children and teens from 16 potentially harmful diseases. This is a good time to remind parents that vaccines are safe and effective -- the odds of having an anaphylaxis-related reaction following the administration of a vaccine are very slim," said study author Dr. Michael McNeil, of the CDC.

For the study, the researchers reviewed records from more than 17 million visits and more than 25 million administered vaccines. The vaccines were given from 2009 to 2011.

The researchers identified 380 cases of anaphylaxis, possible anaphylaxis, or allergy. Only 135 of these cases involved children aged 5 years old or younger, the researchers said.

Results of the study were published recently in the Journal of Allergy and Clinical Immunology.

"We identified no cases of anaphylaxis in children less than 4 years old. The median age of our case patients was 17 years old with a range from 4 to 65 years old," McNeil noted in a journal news release.

None of the people who had anaphylaxis died, and only one had to be hospitalized, the study found.

Pre-existing allergies, asthma or past anaphylaxis were a factor in 85 percent of these cases, the study found. The researchers pointed out that these medical issues are known risk factors for anaphylaxis.

Life-threatening reactions are rare following immunization but caregivers should always be prepared to treat symptoms of anaphylaxis. The study noted that epinephrine -- the first-line treatment for anaphylaxis -- was given in only 45 percent of these cases.

Only 9 percent of those who had a serious allergic reaction had a documented prescription for an epinephrine auto-injector, the study found. After the reaction occurred, only 15 percent were known to have been referred to an allergist for follow-up.

More information

The U.S. Centers for Disease Control and Prevention provides more information on vaccine safety.